1. Field of the Invention
This invention relates to telescopically engaging oil field bore hole containing apparatus and insertion apparatus with sealing means between them.
2. Description of the Prior Art
Various means have heretofore been used to seal around pipe hangers in a wellhead as, for example, the O-rings and packing elements of elastomeric material as shown in U.S. Pat. No. 2,830,665 Burns et al.
Recently, however, oil wells having bottom hole pressures of as high as 30,000 pounds per square inch have been encountered, and such seals as have previously been used have not been capable of holding such pressures. Additionally, underwater well completions require reliable seals of the metal-to-metal type instead of the elastomeric type which break down from subjection to chemicals, heat, or water for sustained periods of time.
Metal-to-metal seals of various kinds have also been used in many installations, including in wellheads. For example, the aforesaid patent to Burns et al shows the use of a metal ring gasket between two flanges of the christmas tree construction shown there.
One form of metal-to-metal gasket which has heretofore been known is that shown in U.S. Pat. No. 2,992,840 to Reynolds et al, which discloses a metal gasket which is frusto-conical in cross section and which is compressed between two flanges having a greater cone angle so that the gasket is deformed, the edges of the gasket being "coined" so as to closely engage elements of the flanges and provide a metal-to-metal seal.
Gaskets which apparently function similarly to those shown in the Reynolds et al patent are manufactured and sold by Aeroquip Corporation of Los Angeles, Calif. under the trademarks CONOMASTER and CONOSEAL.
None of the aforesaid sealing systems has been capable of dependably providing a seal under pressures as high as 20,000 psi, much less 30,000 psi or higher. Furthermore, sealing systems such as that shown in the Reynolds et al patent are objectionable because the gaskets may work-harden and cause damage to moving sealing surfaces. They also do not dependably seal against pressures from either direction, as required in pipe suspension apparatus. Additionally, they are objectionable because of difficulty in installing such a gasket in a well pipe suspension apparatus, where the gasket must be installed in an inaccessible location.
Remote sealing, stab-in devices for automatic telescopic sealing engagement with bore holes are also known in the art. These devices normally provide for vertical insertion and are of two types. The first type employs remote connectors that pull the devices into the bore holes, or otherwise pull or push the devices and the apparatus having the bore hole together to activate the seal. The second type employs the weight of the device inserted into the bore hole to effect the seal. These techniques of sealing, however, require close vertical tolerance to insure, for example, the formation of metal-to-metal seals between pack-off nipples and tubing hangers as the pack-off nipples are inserted into the tubing hanger. The close tolerance of the vertical spacing, for example, between the top of the tubing hanger and the top of the wellhead, is very difficult to control because, for example, the wellhead rests on an outer casing hanger of a series of casing hangers which rest on one another, while the tubing hanger rests on the inner casing hanger of the series of casing hangers. Any mud or other contamination between the casing hangers at the point of support will therefore change the vertical spacing between the tubing hanger and the top of the wellhead. Unlike the present invention, none of the aforesaid sealing systems is substantially free of the requirement for close vertical tolerance.